FLUID INCLUSION STUDY OF GYPSUM PRECIPITATED IN ACID SALINE WATERS: PRELIMINARY RESULTS FROM MARS-ANALOG SALAR IGNORADO, NORTHERN CHILE

Salar Ignorado is a salt flat which occupies an area of ~0.7 km²at 4200 m elevation surrounded by active volcanoes of the Andes Cordillera of northeastern Chile, where there is little, if any, atmospheric precipitation. The salar contains shallow pools of acid saline waters with pH of 3.3-4.6 and salinities up to 3 % TDS. Ignorado pools, located in depressions on the wind-scalloped salar, precipitate gypsum, jarosite, and hematite. The source water of these acid pools is unknown, but is likely volcanogenic. The mineral assemblage, volcanic setting, acid saline waters, and windy, hyper-arid climate make this an excellent terrestrial analog for Mars.

Abundant bottom-growth gypsum crystals at Salar Ignorado contain fluid inclusions that record environmental conditions in the salar. Petrographic observations with plane transmitted, reflected, and polarized light, and UV-vis epi-fluorescence show that triangular, horn-shaped, and sub-rectangular primary fluid inclusions contain waters, air bubbles, prokaryotes, algae, and organic compounds. Some inclusions with possible cellular material contain micrometer-scale clear, spherical solids. Laser Raman spectroscopy with 532 nm excitation shows that these spherical solids are high molecular weight alkane-rich hydrocarbons with variable fluorescence intensity. Study of extremophile microorganisms and organic compounds from this terrestrial Mars-analog environment, and their style of preservation within the rocks, may lead to improved methods for the search for past life on Mars.